Lecture 5 - The Peripheral Nervous System Flashcards
What kind of neurons does the Somatic Nervous System contain? (voluntary)
- sensory neurons (afferent)
- somatic motor neurons (efferent)
What do sensory neurons do?
convery input from receptors for somatic senses and receptors for special senses
What do somatic motor neurons do?
innervate skeletal muscles
What does the autonomic nervous system do? (involuntary)
- regulates cardiac muscle, smooth muscle, and glandular tissue
- autonomic motor neurons regulate visceral activities by exciting or inhibiting activities in effector tissue
Somatic sensory vs visceral sensory (afferent divison of PNS)
- somatic sensory: carries signals from receptors in skin, muscles, bones and joints
- visceral sensory: carries signals mainly from organs in the thoracic and abdominal cavities
How many neuron systems are there in the somatic vs autonomic nervous system?
- somatic: 1
- autonomic: 2
Somatic neuron system
starts at spinal cord -> somatic motor neuron -> effector (skeletal muscle)
Autonomic neuron system
starts at spinal cord -> preganglionic neuron - > ganglion -> postganglionic neuron -> effectors (smooth muscle, glands, cardiac muscle)
General sensory receptors by structural class
- free nerve endings
- encapsulated
- proprioceptors
Free nerve ending: of sensory neurons: functional class by stimulus type
- nociceptors (pain)
- thermoreceptors (heat and cold)
- mechanoreceptors (pressure)
- chemoreceptors (changes in chemical compositions)
Free nerve ending: of sensory neurons: body location
- most of the body tissue; most dense in connective tissue
Modified free nerve endings: (Merkel discs): functional class by stimulus type
mechanoreceptors (light pressure)
Modified free nerve endings: (Merkel discs): body location
deepest layer of epidermis
Free nerve endings: hair follicle receptors: functional class by stimulus type
mechanoreceptors (hair deflection)
Free nerve endings: hair follicle receptors: body location
in and surrounding hair follicles
Encapsulated: tactile (meissner’s) corpuscles: functional class by stimulus type
- mechanoreceptors (light pressure, discriminative touch, vibration of low frequency)
Encapsulated: tactile (meissner’s) corpuscles: body location
hairless skin, particularly nipples, external genitalia, fingertips, eyelids
Encapsulated: lamellar (pacinian) corpuscles: functional class by stimulus type
- mechanoreceptors (deep pressure, stretch, vibration of high frequency)
Encapsulated: lamellar (pacinian) corpuscles: body location
- dermis and hypodermis; most abundant on fingers, soles of feet, external genitalia, nipples
Encapsulated: ruffini corpuscles: functional class by stimulus type
- mechanoreceptors (deep pressure and stretch)
Encapsulated: ruffini corpuscles: body location
deep in dermis, hypodermis and joint capsules
Proprioceptors: muscle spindles: functional class by stimulus type
mechanoreceptos (muscle stretch)
Proprioceptors: muscle spindles: body location
skeletal muscles; particularly those of the extremitites
Proprioceptors: tendon organs: functional class by stimulus type
mechanoreceptos (tendon stretch)
Proprioceptors: tendon organs: body location
tendons
What are the purposes of the spinal cord? (4)
- communication system between brain and various parts of the body
- essential for voluntray and involuntary actions
- highways for sensory and motor integrations
- important for rapid automatic responses through reflexes
What are the roles of the spinal cord?
- provide structural support
- protection
- organization of nerves
What are the 3 layers of the spinal cord (from outside layer to inside the nerve fiber)
- epineurium
- perineurium
- endoneurium
How many pairs of spinal nerves are there?
31
What is special about spinal nerve pairs 1-7?
they leave the spinal cord above their corresponding vertebrae level
Classify the 31 spinals nerves into their groups
- 8 pairs of cervicle nerves
- 12 pairs of thoracic nerves
- 5 pairs of lumbar nerves
- 5 pairs of sacral nerves
- 1 pair of coccygeal nerves
What do each spinal nerves connect to the spinal cord throuhg?
dorsal root
What do dorsal roots contain?
- axonal processes of sensory neurons arising from posterior horn
- dorsal root ganglion
What is the dorsal root ganglion?
- enlargment of dorsal root
- cluster of cell bodies of sensory neurons
- functions as sensory relay stations by processing and modulating sensory signal before reaching the CNS
Where do the spinal nerve and the dorsal root ganglion lie within?
the intervertebral foramina
What does the ventral root contain?
- axonal processes of motor neurons whose cell bodies are locted in the anterior horn of the spinal cord
What does each spinal nerve branch into? (2)
- dorsal ramus
or - ventral ramus
What do the dorsal and ventral rami have in common?
- contain sensory and motor fibers
- exit the vertebral column through the intervertebral foramina
- supply the entire somatic region of the body
What are the differences between dorsal and ventral rami?
- dorsal rami: supplies dorsum of neck and back
- ventral rami: supplies andterior and lateral regions of neck and truck, and all regions of the limbs. It is also much thicker than the dorsal rami
How do the ventri rami travel?
- they brand out extensively to form complex networks known as nerve plexuses (rather than travelling directly to their target issue)
How many primary nerve plexues are there from the ventral rami?
4
the nerve travel to specific target tissue to facilitate motor control and sensory perception
What are the nerve plexuses of the body?
- cervical
- brachial
- lumbar
- sacral
Cervicle plexus
- spinal nerves C1-C4
- supplies sensory and motor innervation to the neck and portions of the head
Bracial plexus
- spinal nerves C5-T1
- supplies sensory and motor innervation to shoulders and upper limbs
lumbar plexus
- spinal nerves L1-L4
- supplies nerves to the lowerback, abdominal wall, and part of the lower limb
Sacral plexus
- spinal nerves L4-S5
- innervates the buttocks, pelvic structures and the remainder of the lower limbs
What are dermatomes?
- sections of the skin innervated by a single spinal nerve
- motor and sensory innervation for those specific areas
what are th etwo important dermatomes?
- T4: nipples
- T10: Umbillicus
Anatomy of the motor reflex arc
- sensory recptor
- sesnory neuron (afferent)
- dorsal root ganglion
- dorsal root
- posteior horn
- interneurons
- anterior horn
- motor neuron (efferent)
- effector muscle
